Electricity meter reading technology has developed in recent years to include, in addition to traditional manual reading of a meter dial, a capability for remote reading. In a customary remote reading arrangement, optical sensing of the meter rotor is performed. Control circuitry is provided for sensor energization and detection, and correlation thereof to power usage. Signals indicative of power usage are transmitted to a remote location of the utility company.
Meters generally are enclosed as a unit within a housing which is provided with a plug to be inserted into a socket of a base. The meter is connected electrically between the utility company power supply side and the user, or customer, power supply side, both connections being made through the base. Such an arrangement is exemplified by U.S. Pat. No. 4,588,949, issued to Becker et al. on May 13, 1986. Automatic meter reading utilizing an optical shaft encoder with appropriate control circuitry is illustrated in U.S. Pat. No. 4,665,359, issued to Goodwin on May 12, 1987.
In recognition of the concern of electric utility companies to avoid the theft of electricity, some conventional meter systems include provisions for attempting to determine whether tampering with an electricity meter by unauthorized personnel has occurred. Electricity meters which contain electronic circuitry may contain a position sensitive switch to sense removal of the meter from its socket. The meter of the above-identified Becker et al. patent includes such a device. In the Becker arrangement, removal of the meter and reinstallation thereof actuates a solenoid which results in visual indication within the meter display of the unauthorized removal.
As meter reading systems have become more sophisticated, it has been advantageous to house the electronic control circuitry in the meter socket base or an extension thereof. Such placement enables easier access to the circuit elements in comparison to the enclosed meter housing which is preferably standardized and may be limited in space to include only the structural elements of the meter.
A disadvantage with the placement of electronic components in a base outside the meter is that no position sensitive switch, such as provided by the Becker device, or other tampering indicator is available in the meter. If a position sensitive switch is provided instead in the base, additional components must be made available for indication of the tampering condition. Moreover, a position sensitive switch, which can determine close structural engagement between the meter and base, would not indicate that the connection between meter plug and base socket is made in proper orientation. For example, if there is an unauthorized removal of the meter and then reinstallation in reverse connection, only the removal would be indicated. Power usage during such a connection would drive the meter rotor in a direction opposite to the appropriate direction. An actual decrease in the power usage display would occur. Manual meter reading by the utility company at a later time would not reveal this condition.
In the Goodwin meter, tampering is detected by comparing the quantity displayed with the encoded values in the optical encoders. Other tamper prevention or detection schemes involve visually discerning the rupture or breakage of a structural element, such as a lock or seal, associated with the meter housing and base. Discovery of tampering with such meters requires the physical presence of personnel at the meter sites, a disadvantage in terms of cost and time consumption.